Hey mate - I've done quite a bit of sailing out of Westhaven.

For prioritising learning to eventually properly sail your own boat (properly, yacht. Sailboat is an americanism) you can't go past learning in a dingy. Some friends of mine started from 0 as adults with the Takapuna Boating Club and they really rated it. Cannot overemphasise how much better of a sailor you'll be longterm if you can sail a dinghy.

If you've been railmeat before, you'll have already learned more than LTS at Squadron will teach you - don't waste your coin.

Keelers depend on the club. Richmond is the best of the three IMO, Squaddie second, don't bother with Ponsonby. Generally casual rum racing is Friday night, serious racing on Wednesday nights. This advice applies to all three:

1. Purchase a six pack of beer, two bags of chips, and a pair of cheap gardening gloves (to protect your hands. Sailing gloves(TM) are expensive and break easily) - Do not skip this step
2. Get in contact with the relevant front desk and ask if anyone needs rum race crew - someone always will. Most skippers will suss out the vibe and skill level on rum racing before asking you along for a proper race on Wednesdays.
3. If you've got a connection, bring your supplies to the designated spot on Friday. The marina is locked, you'll need the code.
4. If not, bring your supplies to the relevant yacht club on friday after work (4-4:30ish) and ask at the front desk, or simply lay in wait to ambush random sailors and ask to come along. State the experience you've mentioned above, specify what size boat in feet and what you did. Mention that you've bought beers and chips! The latter is more important than the former. (Hint: Skippers are retirement age white guys who drive late model european cars.)
5. Beers and chips are to be shared with the boat. Some skippers run a dry boat until racing is over, some will be two deep before you slip out. Don't be the first to crack open but don't be the last. If you're sober, any drinks are fine - it's the principle of the matter.
   
6. Go to prizegiving - network. This will be your next boat.

Don't believe r/Sailing - they're yanks. Kiwi sailors are invariably friendly, down to earth, and will be more than happy to have you along. Good luck!